Brakes, for instance.  My current brakes do kinda sorta stop the bike, but only after a generous application of both sets.  The back tire brakes don't stop the bike alone, while the front ones do, which isn't actually that fantastic because using just them would send me over the handlebars.

I have biked over 250 miles with the brakes like this, but enough is enough.  I now have gotten to the point where I have to anticipate every stop well in advance and coast to it, which is the biking equivalent of down-shifting... at least on flat ground.  Coming down a hill is a different matter entirely.

Next: fenders!